Abstract
Abscisic acid (ABA) plays primary regulatory roles in the plant's response to some stresses. The purpose of this study is to know the regulatory mechanism of ABA on growth and development of cucumber plants (Cucumis sativus L. cv. Hokushin) grown under low nitrogen conditions. Endogenous levels of free ABA in the aerial parts, not in roots, of cucumber plants grown under low nitrogen conditions substantially increased as compared to those grown in normal nitrogen conditions. On the other hand, endogenous levels of conjugate ABA in the aerial parts of the plants grown under low nitrogen conditions were almost same as those in normal nitrogen conditions except in the plants treated with relative high concentration of ABA. No phaseic acid detected in cucumber plants irrespective of the growth conditions. These results suggest that cucumber plants grown under low nitrogen conditions suppress the growth by increasing endogenous levels of free ABA.
